The invention relates to microcapsules with a polymeric capsule wall.
Microcapsules of this type, processes for their production and various possible uses are disclosed in "Angewandte Chemie", 1975, No. 16, pages 556 to 567. According to this publication, microcapsules are taken to mean particles having a size on the order of from 1 to 5000 microns which comprise a core and a solid capsule wall. According to the intended use of the microcapsules, the core contains an active substance which is insulated from the capsule environment by the capsule wall, and can be released to the environment in a specific manner by destruction of the capsule wall or by permeation. The capsule wall comprises, in particular, natural or synthetic polymers whose type, together with the thickness of the capsule wall, on the one hand, determines the outer shape of the microcapsules as spheres, botryoidal aggregates or irregular structures and, on the other hand, determines the ability of the capsule wall to insulate and liberate the capsule contents in a specific manner. The capsule opening can be effected mechanically from the outside, by shearing or crushing, or from the inside, for example by heating to above the boiling point of the capsule contents, by dissolution, melting or combustion of the capsule wall.
Known microencapsulation methods are mechanical-physical and chemical processes. The latter includes interface polycondensation, in which a first monomer, dissolved in a water-immiscible solvent, is dispersed in a water/protective colloid solution with vigorous stirring; when a second monomer dissolved in water is added, the two monomers react at the solvent/water interface to form a solid polymer (polycondensate) in the form of microcapsules containing the solvent.
A known use of microcapsules is in reaction copy papers, for example of the "self-contained type", which are coated on one side with microcapsules containing a color former and with a developer substance. At the points where the microcapsules are destroyed by the pressure of a writing implement, a visible mark immediately appears due to the color former which is developing.
A further use of microcapsules is disclosed in GB-A-2,173,452 in combination with an image-recording process in which the ink-containing microcapsules are applied to a recording carrier and are broken open, or at least rendered ink-permeable by a laser beam, so that the ink reaches the recording paper in accordance with the image to be recorded. There is no indication in GB-A-2,173,452 of how this is actually achieved and which capsule wall materials may be suitable for this purpose.